Curing processes of radiation curable resins and resin compositions are resource-saving and energy-saving and films having excellent properties can be obtained. Therefore, application thereof has been developed in various adhesives, coating agent, inks, coating compositions, binders for magnetic recording media and the like.
Particularly, radiation curable urethane resin has good properties such as good curing characteristics by radiation, toughness of a film obtained by curing and the like and, therefore, it has been studied in the above various fields (for example, see Japanese Patent Kokai No. 52-17517, U.S. Pat. No. 4,082,634, U.S. Pat. No. 4,097,439, U.S. Pat. No. 4,552,932, Canadian Patent No. 1,192,330 and European Patent Published Application No. 0 264 551 A).
However, the conventional radiation curable urethane resin or its composition having good curing characteristics by radiation has a drawback that radicals are liable to be formed, which results in poor storage stability. Further, among properties of a film obtained by curing, regarding solvent resistance, boilproof properties, weather resistance and stain resistance, any radiation curable resin having sufficient properties has not been found heretofore in the prior art.
Recently, there has been a great increase in a demand for precoated metals in various products for indoor applications such as household electric appliances, for example, refrigerators, washing machines and the like, business machines, interior construction materials as well as products for outdoor applications such as roof covers and side walls of houses and the like. In these fields, a radiation curable coating composition which satisfies the above solvent resistance, boilproof properties and weather resistance has also been desired. However, any coating composition having sufficient properties has not been found in the prior art, either.
Among the conventional precoated metals using thermoset coating compositions which have been widely used, particularly regarding precoated metals used for indoor products, color layers to which various pigments are added are formed on their outermost layers from the viewpoint of design. However, with such a technique, properties and appearance of the products are limited. Therefore, it has been desired to develop a precoated metal which overcomes the above limit in the conventional precoated metals.